Digital print-producing apparatus on a photographic basis, so-called digital photographic printers, produce prints or copies by projecting the image information of the underlying original present in electronically stored format onto a photo sensitive copy material. One possibility therefor consists in that the image information of the original is optically represented as an image by way of an appropriate electro optical, pixel-wise operating converter device, i.e., to produce an optical representation of the original and to project this optical representation of the original onto the copy material and thereby expose it thereonto. As electro-optical converter devices can thereby be used both active (self-illuminating), as well as passive (modulating) electro optical arrangements; typical examples are cathode ray tubes, liquid crystal cell fields operated in transmission or reflection mode, light emitting diode fields, electro luminescence cell fields and lately also so-called digital micro mirror fields.
One deciding factor for the quality of photographic pictures or copies made in this manner is the resolution (pixel number) of the electrooptical converter device used. While smaller converter devices of sufficiently high resolution are available at economically justifiable prices, the development of economically producible and commercially useable large surface converter devices of corresponding resolution is still in the beginning. Thus, with the available converter devices, only pictures of relative small format can be produced with satisfactory quality.
Through line-by-line or strip-wise projection, theoretically, arbitrarily large photographic pictures can be produced in direction transverse to the lines or strips.
Only strip-shaped sections of the original which in their longitudinal direction cover the whole original are hereby sequentially optically depicted and sequentially projected onto the copy material in a corresponding spatial relationship. The correct spatial positioning of the projected strips is thereby caused by relative displacement of the copy material relative to the path of the projection light path. The latter can be achieved by advancement of the copy material or by a correspondingly moveable projection optics. The relative displacement occurs of course synchronously with the change of the projected strips of the original. If the strips are several lines wide, adjacent strips can also overlap. Since the copy material is multiply exposed, depending on the degree of overlap, this must be correspondingly considered for the adjustment of the amount of copying light for the individual exposure steps. This exposure process is commonly known under the designation TIG (Time Integration Grayscale).
For this process of the line-by-line or strip wise projection comparatively favourable linear converter devices can be used. Under that, one understands rectangular converter element arrangements (fields), the width of which is significantly smaller than their length. In the extreme case, such a linear converter device includes only a single row (line) of converter elements, typically, however, up to several hundred rows. In longitudinal direction such a linear converter device typically has one thousand or more converter elements (per row or line). Of course, wider converter devices (with a higher number of rows) can be used, whereby not all rows (i.e., not the whole width) need be used.
With the above-described methods, qualitatively satisfying photographic prints can only then be produced with the use of the commercial converter devices, when the format of the picture to be produced is relatively small in longitudinal direction of the projected strips. The resolution of the commercial, economically acceptable converter devices is, however, in many cases insufficient for print formats which are also larger in the other dimension.